Police and demonstrators expect clashes tomorrow as 1,400 officers from 26 forces try to prevent up to 2,000 climate change activists from closing down the Kingsnorth coal power station, run by energy company E.ON in Kent.

Today neither group would say how they were planning to outwit the other. A spokeswoman for Kent police said: "We are expecting the unexpected. Our preparations are constantly changing."

The campaigners have spent the last week encamped near the power station preparing for the direct action protest against plans for a new coal power station at Kingsnorth.

They intend to approach the power station by air, sea and land. One group intends to head up the road directly to the main gate of the power station. Another will approach through the undergrowth in small groups. A third will be making an airborne approach by means that have as yet remained secret. And people on rafts and boats will be sailing up the estuary in an armada to lay aquatic siege.

But the authorities yesterday tightened their squeeze on the protests by formally banning the flotilla. Medway Ports Authority, using bylaws, declared the water-borne protest illegal on safety grounds.

The campaigners argue that because coal produces significantly more carbon dioxide than other means when generating electricity, the station at Kingsnorth coal must not be given the go-ahead. It would be the first new coal station in 30 years and herald a new generation of stations. Supporters of the plans say the UK faces a huge energy gap if coal stations are not allowed and that future carbon capture and storage technology can bury up to 90% of emissions.

Others, saying that the proposed new Kingsnorth power station will produce twice as many climate-harming emissions as the proposed third runway at Heathrow, demonstrated at the Royal Bank of Scotland. A third group went to Windsor where power company E.ON sponsors a Lego model of Kingsnorth power station. Other protests have been held at Gatwick airport and at a biofuel depot at Thurrock.

The climate camp has been marked by angry accusations that the police have used aggressive stop and search powers to disrupt the camp and "smear" the protesters. Yesterday, MEP Caroline Lucas and MPs Norman Baker and Colin Challen wrote to the Kent police pleading with assistant chief constable Gary Beautridge, in charge of the police operation, to resolve "an increasingly threatening confrontation".

"Climate change must be a wholly legitimate subject of protest and demonstration. But if it is met by an arbitrary, destructive and aggressive police response, the consequences will undoubtedly be a continued alienation between police and many decent, law abiding people, particularly the young", said the politicians.

On Thursday, police had stop and search powers extended to the whole of the Hoo peninsula, where Kingsnorth is sited. Kent police said the decision had been taken because officers continued to find people carrying potential weapons, a charge that was angrily denied by the camp.

"What we are doing is part of a long tradition of civil disobedience" said Maria Romero, one of the camp press team. "We're not blasé about breaking the law, but the threat that new coal poses to our future on this planet more than justifies the actions we are taking."

Tensions between police and protesters have been growing throughout the week, with activists angry with what they said were disproportionate searches causing queues of up to two hours to get on site. With helicopters flying low overhead, Paul McLeish, 41, a lawyer and legal observer at the camp, said police had confiscated items including kitchen equipment, children's chalk and crayons, blots for constructing toilets and piping for water on the camp.

"The searches have been absurdly over the top with everything from 26-foot banners to disabled access ramps taken away," said McLeish. " It's a concerted attempt to demonise people and alienate members of the public so they don't think it is safe to come here. It's a depressing a chilling attack on the right to freedom of expression and assembly."

Challen, Labour MP for Morley and Rothwell and chair of the cross-party climate change group, visited the site today. "The climate change debate in the workshop was of a higher calibre than in the House of Commons", he said.

It also emerged that the campers intend to make Kingsnorth a permanent camp. "From the moment the first concrete is poured [to build the proposed new power station] there will be a rolling blockade," said one protester following a large meeting of the camp. Additional reporting by Alexandra Topping